New trends in chemical synthesis involve the use of continuous reaction schemes, for example, in microfluidic and/or millifluidic devices. In many of these processes, it is often helpful to maintain controlled separation between two liquid phases and/or between a liquid phase and a gas phase. For example, in many processes, liquid-liquid and/or a gas-liquid separations are performed (e.g., between an aqueous and an organic phase). In some processes, such as certain membrane reactor systems, separation between two reactant phases and/or between a reactant phase and a product phase is desired. Improved systems and methods for establishing and/or maintaining separation between two fluids would be desirable.